1. Field of the Invention
The present invention relates to a technology for driving a plurality of light-emitting elements with different currents for obtaining predetermined emission intensities.
2. Description of the Related Art
There is a display unit that uses a light-emitting element such as a light-emitting diode (LED), as a light source, for emitting each light of red (R), green (G), and blue (B) colors, drives the light-emitting element in a time division manner, and sequentially emits each of the RGB colors, so that a color image can be projected on the screen. To reduce a circuit scale of the display unit, there is a method of sharing a power supply unit with the light-emitting elements for the colors and sequentially applying a power from the power supply unit to each of the light-emitting elements. In this case, because rated currents required for the light-emitting elements for the colors to emit the lights at predetermined luminance are different from each other, the current to be supplied to each of the light-emitting elements also needs to be controlled at each timing for emitting the respective light.
To control the current to be supplied to each of the light-emitting elements, Japanese Patent Application Laid-open No. 2007-273666 discloses a method of variably setting the current by providing a variable setting unit that variably sets the value of the current to a set current corresponding to each of the light-emitting elements and switching between resistors corresponding to the light-emitting elements using a switching element. Japanese Patent Application Laid-open No. 2007-273666 also discloses a method of supplying a required power to a light-emitting element which has an insufficient power immediately after being switched, absorbing a power of a light-emitting element which has an excessive power, and stabilizing the current flowing through each of the light-emitting elements by charging a voltage appropriate for a drive voltage of the light-emitting element in an auxiliary capacitor and connecting the auxiliary capacitor in parallel to the light-emitting element at a predetermined timing.
According to the conventional technology described above, however, because the set current is changed by switching between the resistors corresponding to the light-emitting elements using the switching element, it is difficult to stabilize an output current at a fast response speed corresponding to a change of a status (current and voltage) of the light-emitting element. Moreover, in the above method, a large capacitance is required when a difference in currents upon switching is large, and thus, responsivity to an output current from the power supply unit is degraded, which makes it more difficult to stabilize the output current at a fast response speed, which leads to an increase of the device in size and an increase in cost.